Thanks Kissmykimchi, the ones labelled as HDR (like these ones here) are processed using a program called photomatix all others may occasionally be cropped or straightened, but otherwise are untouched.

For more info you can read here: http://en.wikipedia.org/wiki/High_dynamic_range_imaging

And the software site is here:http://www.hdrsoft.com/

You just need a camera capable of taking RAW files as well as jpegs to create these effects (I use a Canon 400D).